DESCRIPTION (adapted from abstract): Cilia and flagella are complex microtubular organelles that are ubiquitous among eukaryotes, including humans, where they are found in the respiratory tract, the female reproductive tract and on sperm cells. Ciliary and flagellar dysfunction resulting from the absence of dynein arms has been reported to cause respiratory and fertility problems in humans and other mammals. The long term objectives of this work are to understand the ways dyneins are organized in ciliary axonemes and to understand the role(s) of each different dynein in ciliary motility. This will be done by using targeted gene knockout techniques to introduce mutations into genes encoding dynein heavy chains in the unicellular protozoan, Tetrahymena thermophila. To initiate those studies a mutation was generated in the Tetrahymena DYH6 gene. Initial characterization of this mutant (DYH6 KO) indicates that axonemes isolated form the mutant are missing the two dynein heavy chains that make up 18S dynein. The specific aims of this project are 1) to test the hypothesis that Dyh6p is a component of Tetrahymena inner arm dynein I by determining where 18S dynein is located in the axoneme and by completing the characterization of 18S dynein; 2) to determine the role 18S dynein plays in ciliary motility by determining the frequency of sliding disintegration of isolated axonernes in the absence or presence of trypsin, by determining the rate at which microtubule doublets slide apart during disintegration, and by determining the wave form in mutant and wild-type cilia; 3) by determining the effect of the DYH6 KO mutation on ciliary motility by determining swimming velocity and behavior in mutant and wild-type cells. The results of this work should add to the understanding of dynein organization and function in cilia and flagella.